Friday Illusion: Upright balance beam seems to tilt

Think your eyes can detect if an object is upright? A new illusion by video producer Greg Ross shows that it's not always the case as visual detail can sometimes fool our brain.

In this video, a balance beam is filled in with a diagonal pattern. Does it seem to be skewed? Keep watching as the lines are slowly removed. Do you notice a difference when the drawing is white?

The balance beam should look tilted when it's covered with lines but upright when they are erased. However, measuring the distance between the blocks would prove that the top and bottom are parallel in both cases.

According to Ross, the effect is due to the opposing direction of diagonal lines in each rectangle. But the triangle placed on the right side of the top beam accentuates the effect. "We perceive it as weighing down on the right side but only when the diagonal lines are there," says Ross.